Inheritance: BaseModel
 //clears the list of facilites
 //removes a hub
 public void RemoveHub(Hub hub)
 {
     _hubs.Remove(hub);
 }
        public void removeHub(Hub hub)
        {
            Hubs.Remove(hub);
            Airport.RemoveHub(hub);

            CanBuildHub = canBuildHub();
        }
 public void AddHub(Hub hub)
 {
     _hubs.Add(hub);
 }
        public void addHub(Hub hub)
        {
            Hubs.Add(hub);
            Airport.AddHub(hub);

            CanBuildHub = canBuildHub();
        }